1. Field of the Invention
The present invention relates generally to a circuit board structure for electrical testing and a fabrication method thereof, and more particularly to a circuit board structure and fabrication method thereof, wherein distributing wires and a plurality of electroplating conductive wires are disposed in the inner layer of the circuit board structure, and a broken circuit is created in the distributing wires, so as to perform electrical testing.
2. Description of Related Art
The electroplating conductive wire of a multi-layered CSP (Chip Size Package) product is generally formed in the inner layer core board of the product so as to ensure high reliability of the circuit board. Before electrical testing of the circuit board can be performed, the electroplating conductive wire in the inner layer core board must be removed or severed.
Referring to FIG. 1 and FIGS. 2A to 2E, schematic views illustrate a conventional method of breaking individual circuits in order to provide separate circuits.
First, as shown in FIG. 1 and FIG. 2A, a core board 10 is provided, which has a plurality of electroplating conductive wires 11, a plurality of distributing wires 12 and a plurality of circuits 13. The distributing wires 12 electrically connect the electroplating conductive wires 11 and the circuits 13. The circuits 13 further comprise a plurality of electrically connecting pads 131. An insulating protection layer 14 is formed on the surfaces of the electroplating conductive wires 11, the distributing wires 12 and the circuits 13. The insulating protection layer 14 is formed with a plurality of first openings 141 for exposing the electrically connecting pads 131 and a plurality of second openings 142 for exposing a portion of the distributing wires 12.
As shown in FIG. 2B, a resist layer 15 is formed on the second openings 142 in the insulating protection layer 14 to cover the distributing wires 12 but expose the electrically connecting pads 131 through the first openings 141.
As shown in FIG. 2C, a metal protection layer 16 made of Ni/Au, for example, is formed on the surfaces of the electrically connecting pads 131 by electroplating.
As shown in FIG. 2D, the resist layer 15 is removed so as to expose the distributing wires through the second openings 142 in the insulating protection layer 14.
As shown in FIG. 2E, the distributing wires 12 in the second openings 142 are removed by etching so as to create a broken circuit in the distributing wires 12, and thus the circuits 13 becomes an independent circuit, thereby allowing electrical testing to be performed.
However, as the resist layer 15 has to be formed on the second openings and then be removed after the metal protection layer is formed on the surfaces of the electrically connecting pads, thus increasing the process steps and prolonging the process.
To overcome the above drawback, U.S. Pat. No. 6,660,559 discloses a process that removes a conductive wire in the absence of any resist layer, as shown in FIGS. 3A to 3C.
As shown in FIG. 3A, a core board 10 is provided, which has a plurality of electroplating conductive wires 11, a plurality of distributing wires 12 and a plurality of circuits 13. The distributing wires 12 electrically connect the electroplating conductive wires 11 and the circuits 13. The circuits 13 have a plurality of electrically connecting pads 131. An insulating protection layer 14 is formed on the electroplating conductive wires 11, the plurality of distributing wires 12 and the circuits 13. A plurality of first openings 141 are formed in the insulating protection layer 14 to expose the electrically connecting pads 131.
Referring to FIG. 3B, a metal protection layer 16 is formed on the surfaces of the electrically connecting pads 131 exposed from the first openings 141 in the insulating protection layer 14 by electroplating. The insulating protection layer 14 prevents the metal protection layer 16 from forming on the distributing wires 12.
Referring to FIG. 3C, the insulating protection layer 14 is made of a material that can be melted by a laser beam. A predefined region of the insulating protection layer 14 on the distributing wires 12 is removed by a laser beam, so as to form a second opening 142 in the insulating protection layer 14. A portion of the distributing wires 12 below the insulating protection layer 14 is severed, thereby ensuring separation of the electrically connecting pads 131 and preventing short circuit from occurring.
Although the process using the laser beam can overcome the above-described drawback such as an increase of the process steps and the process time, copper residues and high-temperature carbide residues are likely to be found at the cut, and the residues tend to cause micro-short during an AEI (Auto Electrical Inspection) of a product.
Therefore, there is a need to provide a method for separating the circuit from the electroplating conductive wire in a circuit board upon fabrication of the circuit board so as to enable electrical testing, and prevent a waste of material during the fabrication process, high fabrication cost, and long fabrication time.